Regulation of nitric oxide synthase by subcellular targeting and protein-protein interactions

Endothelial nitric oxide synthase (eNOS) is a peripheral membrane protein that converts L-arginine to nitric oxide (NO). Our work has focused on understanding the basic cell biology of eNOS as it pertains to the regulation of NO production. eNOS is co-translationally N-myristoylated (at glycine-2) and pod-translationally cysteine palmitoylated (at cysteines 15 and 26). These lipid modifications are important for eNOS trafficking into the Golgi region and into cholesterol and glycolipid rich microdomains of the plasma membrane, termed caveolae. Mutations of either site influence eNOS trafficking and block stimulated NO release without influencing eNOS activity in broken cell lysates. Since the compartmentalization of eNOS is critical for optimal NO production, we hypothesized that proper subcellular targeting of the enzyme places eNOS is an environment containing NOS regulatory proteins. Indeed, eNOS interacts with many different proteins based on metabolic labeling experiments including a 22 kDa protein identified as caveolin-1 (CAV-I) and a 90 kDa protein identified as heat shack protein 90 (Hsp90). CAV-I negatively regulates eNOS signaling while Hsp90 is a positive regulator. This review will outline recent progress in undemanding the cell biolgy of eNOS and other NOS isoforms.